Diagnostic assays are widespread and central for the diagnosis, treatment and management of many diseases. In that regard, different types of diagnostic assays have been developed over the years in order to simplify the detection of various analytes in clinical samples such as blood, serum, plasma, urine, saliva, tissue biopsies, stool, sputum, skin or throat swabs and tissue samples or processed tissue samples. These assays are frequently expected to provide a fast and reliable result, while being easy to use and inexpensive to manufacture.
One common type of disposable assay device includes a zone or area for receiving the liquid sample, at least one reagent zone, and a reaction zone also known as a detection zone. These assay devices, commonly known as lateral test strips, employ a porous material, e.g., nitrocellulose, defining a path for fluid capable of supporting capillary flow. Examples include those devices shown in U.S. Pat. Nos. 5,559,041, 5,714,389, 5,120,643, and 6,228,660, all of which are incorporated herein by reference in their entireties.
The sample-receiving zone of these assay devices frequently consists of a more porous material, capable of absorbing the liquid sample, and, when separation of blood cells is required, also effective to trap the red blood cells. Examples of such materials are fibrous materials, such as paper, fleece, gel, or tissue, comprising e.g., cellulose, wool, glass fiber, asbestos, synthetic fibers, polymers, or mixtures of the same.
Another type of lateral flow assay device is defined by a non-porous substrate having a plurality of upwardly extending projections configured to induce capillary flow. Examples of such devices are disclosed in U.S. Pat. No. 8,025,854B2, WO 2003/103835, WO 2005/089082, W02005/118139 and WO 2006/137785, all of which are incorporated by reference herein in their entireties.
A known non-porous assay device of the above type is shown in FIG. 1. The assay device 1 has at least one sample addition zone 2, a reagent zone 3, at least one detection zone 4, and at least one wicking zone 5, each disposed on a common substrate. These zones are aligned along a defined flow path by which sample flows from the sample addition zone 2 to the wicking zone 5. Capture elements, such as antibodies, are supported in the detection zone 4, these elements being capable of binding to an analyte of interest, the capture elements being optionally deposited on the device (such as by coating). In addition, a labeled conjugate material, also capable of participating in reactions that will enable determination of the concentration of the analyte, is separately deposited on the device in the reagent zone, wherein the conjugate material carries a label for detection in the detection zone of the assay device.
The conjugate material is gradually dissolved as the sample flows through the reagent zone, forming a conjugate plume of dissolved labeled conjugate material and sample that flows downstream along the defined flow path of the device to the detection zone. As the conjugate plume flows into the detection zone, the conjugated material will be captured by the capture elements such as via a complex of conjugated material and analyte (e.g., as in a “sandwich” assay) or directly (e.g., as in a “competitive” assay). Unbound dissolved conjugate material will be swept past the detection zone 4 and into the wicking zone 5.
An instrument such as that disclosed in US 2006/0289787A1, US 2007/0231883A1, U.S. Pat. Nos. 7,416,700 and 6,139,800, all incorporated by reference in their entireties herein, is configured to detect the bound conjugated material in the detection zone. Common labels include fluorescent dyes that can be detected by instruments which excite the fluorescent dyes and incorporate a detector capable of detecting the resulting fluorescence.
In the foregoing devices and in the conduction of assays, the resulting level of signal in the detection zone is read using a suitable detection instrument after the conjugate material has all been dissolved and sample and unbound conjugate material and wash fluid added to a reagent zone of the device has reached and subsequently filled the wicking zone of the device.
Issues may develop using the above stated devices in advance of the completion of the test, for example, due to manufacturing or other defects, which delay, retard or immobilize the movement of fluid in the lateral flow assay device. To that end, it would be beneficial to determine the presence of such error conditions proactively. In addition, there is a general need in the field to improve the efficiency and efficacy of lateral flow assay devices, such as those described above, for example, to determine latent errors in the device or in process flow prior to analyte testing.
In addition, the lateral flow assay device may require external operations such as, for example, the introduction of wash fluid or other reagents, as noted above. It would be beneficial to provide process-related triggers to optimally indicate when this fluid when or should be added.